Instinct
by HikarinRin
Summary: [ONESHOT] MATURE, Alpha/Beta/Omega Dynamics, Heat, First Heat, Incest, Knotting, Self-Lubricant, Alpha!Oso, Omega!Choro, Rough Sex. /
INSTINCT

Pairing : Osomatsu x Choromatsu

Rating : R18+

Series : ONESHOT

Tags : EXPLICIT, Alpha/Beta/Omega Dynamics, Heat, First Heat, Knotting, Self-Lubricant, Alpha Oso, Omega Choro, Rough Sex.

.

.

It's in the midst of summer. The heat from the sun is making the sextuplet sweating like crazy in their bedroom. The Air Conditioner only work in their bedroom, so they got no choice but isolating their self.

Also, it's been a year and a half since they finally knew their second gender. They're splitted in two groups ; Alpha and Omega. Sadly, there's no Beta in Matsuno Family's blood. The Alphas are Osomatsu, Karamatsu, and Jyushimatsu. The Omegas are Choromatsu, Ichimatsu, and of course Todomatsu.

The Omegas heat cycle somehow different every each person in there. The first one that hit the first heat is Todomatsu. Many problems coming after that since Todomatsu letting out strong pheromones around the virgin and unexperienced Alphas, he's also being all moody, all pouty, and... sexy. The biggest problem is Karamatsu. He keeps baring his teeth everytime anyone coming near Todomatsu and he just growls and bark—even to his own parents. His Alpha instinct is just taking a control over him—he declared.

Todomatsu quickly calmed down the day after and his pheromones aren't that strong until 5 days later. Karamatsu told the others that they've mated and he marked Todomatsu, so no Alpha will smell his scent once the heat hit Todomatsu again. They all laughs because THEY NEED TO SLEEP OUTSIDE THE ROOM SINCE THEY TWO MATED IN THE MIDDLE OF THE NIGHT IN THE SHARED BEDROOM BEFORE THE SLEEP TIME AND THEY ALL OUTSIDE ARE FORCED TO HEAR THOSE VOICES.

Same goes to Ichimatsu. The difference is, he keeps mewling and scratching things, being all spoiled and needy. The one who bare its teeth is Jyushimatsu. They've mated and marked, so things are settled up pretty good.

And then, there're left Osomatsu and Choromatsu. Both of them is a late bloomer. Osomatsu hadn't have his rut yet, and Choromatsu hadn't have his first heat yet.

It's all fun and fine until this day.

.

.

Choromatsu reading his Nyaa-chan's magazine like always, but then he notices something. Karamatsu and Jyushimatsu keeps staring at him.

'Huh? What's happening? Why they're staring at me?', he thought.

He took a glance to Osomatsu that's beside Totty. He suddenly widen his eyes and he... growled? He even baring his teeth towards Choromatsu. 'That's rude, nii-san. If you want to ask for Nyaa-chan's magazine, i can lend it to you without you growling at me like that.', he talk inside his head and sighed.

Choromatsu suddenly feel something inside his stomach. It's curling and hot. 'Why am i sweating than usual? Why they keep staring at me..', Choromatsu wheeze as he flaps his magazine to cool down the hot atmosphere around him. 'Ah, maybe buying an ice cream outside won't be too bad.', he said to himself and then proceed to stand up.

Then, he felt something wet and slick around his thighs just a moment before he's fully stand up. Osomatsu, suddenly barked out loud and jumps towards Choromatsu, pinning him down beneath the eldest. Karamatsu quickly holds Osomatsu by hugging him from the underside of Osomatsu's armpits.

"Oi, Osomatsu! Jyushimatsu, help me to carry him out!", Karamatsu said in panic. Osomatsu starts to struggle as he see two alphas inside the same room as Choromatsu. Then, he just struggles and barking, accidentally scratch Karamatsu's arms to blood. But, Karamatsu just won't let Osomatsu out from his arms. Jyushimatsu, with his usual face, pushing Osomatsu out hardly with Karamatsu dragging him. Somehow, Osomatsu's strength overpowering Jyushimatsu, and that's bad.

Choromatsu still laying down there cluelessly. But suddenly, he smell something sweet, masculine, and... demanding. His body start to weakens and his mind is getting hazy. His lower start to prosses more slick by the time Choromatsu whines and panting hardly. He needs something. He feel so empty. He needs something to fill him. He needs it... so bad.

"Totty, Ichimatsu! I'll calm Osomatsu down, so you two help Choromatsu first!", Karamatsu said as he still proceeding to get Osomatsu out. Totty and Ichimatsu nodded and walks to Choromatsu. They held Choromatsu down as he keep moaning and wheezing. His dick also start to throbbing and his hole is just twitching, waiting for that delicious strong scent from... Osomatsu. Yes, he needs Osomatsu. He needs him so bad that it hurts.

"N,No..! Hhah... Osomatsu-niisan...! I need him..! Hhah... Osomatsu-niisan.. Help me... Nngh..Hhah.."

Choromatsu looks at Osomatsu with pleading eyes as his hands reaching out for Osomatsu. He wants it so bad. He wants him. He /wants/ him.

As Choromatsu begging for more, his scent and his pheromones start to hit Osomatsu like a tidal wave. He barks and growls even louder and harder. His Choromatsu is waiting. His Alpha instinct is dragging him. He need his Omega. He /needs/ to fill /his/ Omega.

The other four making eye-contact to each other and they nodded.

"Brother, good luck!", Karamatsu looks at Choromatsu and then he finally freed Osomatsu. The other four quickly runs out from the bedroom and locks it from the outside.

After that, Osomatsu quickly jumps towards Choromatsu. Both of them seems like really loses their minds.

"Osomatsu-niisan...", Choromatsu whines in needy tone.

"Chromatsu. Your scent.. is driving me crazy.", Osomatsu pants and then he buried his face on Choromatsu's neck, smelling that dazzling scent and then he's baring his teeth.

"W, wait-! Osomatsu-nii—", Choromatsu's sentence is being cut down as he yelped from the bite on his neck. Too late, Osomatsu marked him even without asking for his permission first.

It's painful. It's really painful. But.. he want it. He wants more.

Osomatsu just quickly freed Choromatsu's body from the clothes that he wear. He tore it apart. His eyes are shining with lust and needs. He's drunk from Choromatsu's scent and he can't help it.

The heat washed both of their sense and the room is just getting hotter since it's summer.

"Osomatsu-niisan... Hurry..", Choromatsu mewls softly underneath Osomatsu and his hips just start to fidgeting more and more, wanting something to wash this heat off from him.

Osomatsu prods his middle finger against Choromatsu's twitching entrance. It's already self-lubricating so he needs no time to waste. He just pushed two of his fingers inside Choromatsu and he panted even more, feeling the tight and contracting walls around his finger.

In the other hand, Choromatsu moans even louder. It hurts. It hurts so bad. It's stinging and it... feels good.

"More... Nii-san... More.. Ngh..", Choromatsu wheeze and he moans loudly. He start to move his hips to make himself fucking Osomatsu's fingers. He needs something more. More satisfying. Bigger. Thicker. And rougher.

"Hhah... No, Cherrymatsu.. Let me... Prepare you a little bit before i'm really losing my shit.", he laughs forcefully and trying to restrain himself. Something inside him screaming for him to just fuck his younger brother's brain out. Do him mercilessly. Stop preparation. But he just... want to feel it a little more while it's still lucid.

"Nii-san..."

Osomatsu looked up to Choromatsu while his fingers are scissoring and prodding Choromatsu's prostate inside.

"Fuck me, Osomatsu-niisan..."

There's a snap behind his head and that inviting words from this omega... he give up. Choromatsu's opening his arms widely and his mouth is gaping open, moaning softly and wheezing, waiting for his Alpha to knot him.

With that, Osomatsu freed his throbbing dick from his tight jeans. It's throbbing, red, and his precum just flowing out, demmanding to be sticked inside the Omega aching hole.

Choromatsu saw that size of his eldest brother and he... amazed. It's big and it's delicious. He wants that. His hands reaching out for Osomatsu's dick as his mind getting even darker by lust.

"Osomatsu-niisan... Knot me.. I need that.. Nnhhah... Fuck me, Nii-san.. Fuck me..", Choromatsu start to whines even more.

"Calm down, baby. I'm going to fuck you so hard that when the heat is gone, you forgot how to walk."

Osomatsu spread Choromatsu's legs widely and then he lined up himself infront of the omega's needy hole. Without even waiting, he thrust all of his length into Choromatsu, reaching deep inside him.

Choromatsu tilt his head to the back and he gasped for air. The feel of being filled completely making him begging even more.

"Nnghah-! Nii-san! Ah! M-More!"

Choromatsu mewls and moaning in pleasure as his body start to relax and succumb to the heat fully. Choromatsu wrap his arms around Osomatsu and kissing the alpha's neck hungrily, wanting to feel that scent that making him dizzy and addicted.

"Fuck, Choromatsu. Fuck"

Osomatsu start to lose his sense and the beast inside him just finally popped up. His hips movement getting even rougher and rougher, going deep inside Choromatsu and ramming his omega's prostate mercilessly. He panted and growls deep inside him. The pleasure to finally have his own Omega is really blissful. The scent that Choromatsu keep producing is delicious and attracting him more and more.

"Ah! Nii-san! I-i'm coming-!"

Choromatsu screams as he arched his back. He scratch his brother's back with his nails and even drawing some blood out. The pleasures are just unbearable.

"Hhah.. Come for me, baby."

Osomatsu whisper in a really low, commanding voice. The Alpha sense that bursting out from Osomatsu's pheromones making Choromatsu shudders in submissiveness. After the last thrust, Choromatsu screams in pleasure and calling Osomatsu's name as he tilt his head to the backward. He finally had his first orgasm and it feels so great. The semen splatter all around his chest and his stomach.

His walls contracting around Osomatsu's length and it's making the alpha crazy. It feel so good. Oh, he want to bang Choromatsu really bad.

Taking many deep breath, Choromatsu trying to come down from his high as Osomatsu still thrusting into him, ignoring his oversensitiveness due his orgasm. It's still not enough. He wants the knot. He wants it and this is not enough.

"Osomatsunii-san... I—"

"I know. I'm not done with you. Get on your knees and hands."

That commanding tone making Choromatsu limply pulling himself away from Osomatsu, whines when he felt that his hole is empty again. He gets on all four with his butt rising up in the air. His cheek pressed against the futon and he looks at Osomatsu while wiggling his hips.

"Nii-san.. Hhah.."

"Good boy."

Osomatsu grip Choromatsu's hips and then he slam his dick all inside Choromatsu's hungry hole again.

"Ahhn—! Osomatsunii-san..! Ah! Nnhah!"

Choromatsu want to scream louder if it's possible. It feel so good and it's driving him crazy. Osomatsu thrust even deeper because this position is easier for him. The naughty noises between wet skins slap against each other and the moans also the groans filling out the room so bad. The room smell like sex, heat, and pheromones.

Osomatsu start to feel something growing and Choromatsu immediately know it. It's the knot. It's the knot that Choromatsu has been dying from the start they mated.

"Osomatsunii-san! Give me! A,Ah! Give me that! Hhn!"

His sentence almost messed up pretty bad, but of course the Alpha understand the needs of his Omega.

"Yes, Choromatsu, my baby. I'll give it you. Calm down"

He said but he knows that NO ONE of them that's calming down. The heat is just rising and rising. Once the knot finally appeared, he needs to take a few hard thrust against it.

It hurts for Choromatsu. It's way bigger than Osomatsu's dick that's already big enough that it hurts and feels good. But he want that. He want that so bad.

After a few hard thrust, Osomatsu finally thrust his hips really hard that Choromatsu screaming in both pain and pleasure when the knot finally inside and hit his prostate.

Osomatsu move his hips even eager and eagerly. He finally notices that he's ready to spill his love seed into his Choromatsu. And with the prostate stimulation, Choromatsu can feel the wave of his second orgasm in his stomach. Osomatsu's grip on Choromatsu's hips even tighter, making his pace even harder, faster, and messier if that's all are possible.

"Shit.. Hhah. Choro... I'm close.."

"Ah! Nii-san! Nngh! Give it! Fill me, Nii-san!"

Choromatsu screams even louder as his fingers are white because he clences the bedsheet really hard.

After a few hard thrust, Choromatsu finally spurting out his orgasm and jolting as his mouth is gaping open from the lack of oxygen in his lungs that can't keep up with his heat. Osomatsu forcing Choromatsu's hips to stay in balance so he can fuck him a little bit more.

And then, Osomatsu bury all of his knot inside Choromatsu and spill his semen into Choromatsu. He stay in his place as he groans and growls in pleasure. Choromatsu can feel it. The hotness and thickness of Osomatsu's semen that can't stop flowing and filling him eventually.

Choromatsu flops on the futon followed by Osomatsu that's still inside him. The knot needs its time to seathed a bit for him to be pulled out.

Osomatsu lay on the futon beside Choromatsu and pull him into a spooning cuddles. Choromatsu's face are still red from the exhaust and both of them are sticky from the sweat and the total mess that Choromatsu made.

"Choro.. Turn around."

Choromatsu limply and placing his legs over Osomatsu's waists because the knot still connecting them.

"I even haven't kissed you yet."

Osomatsu laughs tiredly and he looks at Choromatsu. Choromatsu can't even let any single word coming out from his mouth. It's tiring. It's sore. And he's happy that his mate is actually Osomatsu. He opens his mouth and looking at Osomatsu.

Of course, Osomatsu understand that hint and he give the omega a peck on the lips, followed by a deep kiss and passionate kiss. Both of them moans between the kisses, and Osomatsu use that moment to slide his tongue into Choromatsu, tasting his omega thoroughly.

After 20 minutes of just hugging, kissing, and admiring each other, the knot finally swell down and Osomatsu pull his dick out from Choromatsu, greeted with the whine of the omega. Choromatsu feel that his hole is empty and its starting to sore. But he knew that the heat wave is going to hit him in another few hours.

"Na, Choromatsu. We're official aren't we?"

Choromatsu nodded tiredly as his eyes starting to blink and he tried his best to preventing himself from falling asleep.

"Now, how about we get a little sleep? I'll wake you up once the heat comes again."

Choromatsu started to panicked and he finally can squeezed a little whisper out from his mouth.

"B-but.. will you be .. there..?"

Osomatsu widen his eyes and burst into a laughter.

"Of course, baby. You're my mate and you're all mine. I won't leave you like this. Now, go sleep."

Choromatsu smiles weakly and then he shift himself inside Osomatsu's arms, feeling safe, and then both of them falling asleep, waiting for the next heat wave.

.

.

"Ugh. We should sleep here again?", Todomatsu looks at the tatami on their living room and he can't imagine sleeping on something that might hurt his body.

"Shut up, Totty. When your heat wave comes again, you're going to sleep on the futon alone with Karamatsu for days and we all gonna suffer here again.", Ichimatsu replied and then he curl himself like a cat in a nest inside Jyushimatsu's arms.

"Totty! Totty in heat? Messy!", Jyushimatsu still as lively as ever and his grin just can't stop showing.

"Oh, brother. I can let you to sleep in my arms if you're sc—"

"Oyasumi.", Todomatsu ignorantly cut Karamatsu's sentence and he just lay beside Karamatsu's leg.

"Eh?"

And there Karamatsu, standing up puzzled.

.

.

FIN. 


End file.
